The present invention relates to contactless integrated circuits comprising means for sending/receiving data by inductive coupling. The present invention particularly, but not exclusively, relates to contactless integrated circuits provided for receiving data coded in accordance with the ISO/IEC 15693 standard or the ISO/IEC 14443-B standard.
In recent years, contactless integrated circuits have considerably developed and methods for transmitting data by inductive coupling, implemented by these integrated circuits, are currently the subject of various protocols, some of which are standardized.
FIG. 1 represents in block form a classical contactless integrated circuit IC1 architecture. The integrated circuit IC1 comprises a coil antenna L1 together with a capacitor C1 in parallel to form a resonant antenna circuit. These elements are sometimes outside the silicon wafer of the integrated circuit. The integrated circuit IC1 also includes a rectifier circuit PSC and a clock extraction circuit CEC1, that are both connected to the coil L1.
When the integrated circuit is immersed in an oscillating magnetic field emitted by a contactless integrated circuit reader (not represented), an induced alternative voltage Vi appears at the terminals of the coil L1. The circuit PSC delivers, using the induced voltage Vi, a voltage Vcc for supplying the integrated circuit, and the circuit CEC1 delivers the clock signal CK of the integrated circuit, the frequency of which is generally a sub-multiple of the carrier of the magnetic field.
The receiving of data by the integrated circuit IC1 is performed by a demodulator circuit DEMC connected to the coil L1, and by a decoding circuit DECC1. The circuit DEMC demodulates the voltage Vi by extracting it from its envelope and removing the carrier, and delivers a demodulated signal Sd containing data coded according to a determined protocol. The signal Sd is applied to the input of the decoding circuit DECC1 the output of which delivers binary data DTr. The data DTr are sent to the central unit of the integrated circuit, for example a central processing unit UC equipped with a memory MEM.
The sending of data by the integrated circuit is performed by a coding circuit CDC the output of which drives a load modulation circuit LMC connected to the terminals of the coil L1. The circuit LMC comprises for example a switch SW in series with a resistor R. Data to be transmitted DTx, delivered by the central processing unit or read directly in the memory MEM, are applied to the coding circuit CDC, the output of which delivers a load modulation signal Slm coded according to a determined protocol, applied to the control input of the switch SW (for example the gate of a transistor). Every time the switch SW is shut off this causes an antenna short-circuit leading to an attenuation of the ambient magnetic field, which is detected by the contactless integrated circuit reader and enables the latter to decode the data sent by the integrated circuit IC1.
As indicated above, contactless integrated circuits are the subject of various protocols, which define the characteristics of the signals intervening in a communication, as well as the coding of the data. The structural differences between two contactless integrated circuits provided to meet two different protocols mainly concern the decoding circuit DECC1 and the coding circuit CDC represented in FIG. 1.
As an example, the ISO/IEC 15693 standard provides for a coding by pulse position modulation of the data sent to a contactless integrated circuit, and a start of frame SOF1 the profile of which is represented in FIG. 2A. The ISO/IEC 14443-B standard provides for an NRZ coding of the data sent to a contactless integrated circuit, and a start of frame SOF2 the profile of is represented in FIG. 2B.
In practice, the provision of these various protocols is justified by technical reasons. Each protocol is provided to obtain determined performances in a determined category of applications. Thus, for example, the ISO/IEC 15693 protocol is suitable for applications requiring a relatively long communication distance and a relatively low data rate, while the ISO/IEC 14443-B protocol is suitable for applications requiring a short communication distance and a higher data rate.
A well-defined type of contactless integrated circuit corresponds to each protocol, which differs particularly from the other contactless integrated circuits by its coding and decoding circuits. The decoding circuit, in particular, includes means for recognizing a start of frame as provided by the protocol.